In an image recording apparatus such as an ink jet printer, when a print start command is given, a record sheet is fed from a tray to a conveying passage. The conveying passage is provided with a roller pair. The roller pair includes a main roller which is rotated and an auxiliary roller pressed against the main roller and supported to be freely rotatable. The main roller is rotated with a record sheet sandwiched between the roller pair, whereby the record sheet is conveyed along the conveying passage. An image is recorded on the record sheet while the record sheet is conveyed along the conveying passage. A related-art image recording apparatus is provided with means for controlling rotation of the main roller. (For example, refer to JP-A-2004-123313 or JP-A-2006-82425)
JP-A-2004-123313 describes an image recording apparatus in which a conveying roller provided upstream from a recording head and a sheet discharge roller provided downstream are joined via a plurality of gears. Thus, a drive force transmitted from a motor to the conveying roller is also transmitted to the sheet discharge roller and the conveying roller and the sheet discharge roller rotate. The image recording apparatus is provided with a rotary encoder for detecting the rotation amount of the conveying roller. Rotation of the motor is controlled based on the detection result of the rotary encoder.
JP-A-2006-82425 describes a printer in which a first conveying roller pair is provided upstream in a conveying passage with respect to a thermal bead and a second conveying roller pair is provided downstream of the conveying passage with respect to the thermal head. The printer is also provided with a first encoder for detecting the rotation amount of the first conveying roller pair and a second encoder for detecting the rotation amount of the second conveying roller pair. A clutch for switching transmission of a drive force from a conveying motor is provided between the conveying motor and the first conveying roller pair and between the conveying motor and the second conveying roller pair. The transmitting passage of the drive force is switched by the clutch, whereby the drive force is transmitted from the conveying motor only to one conveying roller pair and the other conveying roller pair enters a free state in which no drive force is transmitted. In the printer, the rotation amount of the free roller pair is detected by the first or second encoder and the conveying motor is controlled based on the detection result of the encoders. Accordingly, rotation of the roller pair to which the drive force is transmitted is adjusted.
However, in the configuration in which a record sheet is conveyed in one direction by the two main rollers, although the same drive force is given to the two main rollers, the rotation amounts thereof do not match due to the effect of eccentricity or a dimension error of the shaft of the main roller, an attachment error of a drive transmission mechanism for transmitting rotation of the motor to the main roller, and the like. Thus, the conveying distance of a record sheet might change at the change timing from the state in which the record sheet is conveyed by the two main rollers to the state in which the record sheet is conveyed only by the downstream main roller, for example. Consequently, turbulence might occur in the image recorded on the record sheet.